1. Field of the Invention
The present invention relates to ink jet printing, and, more particularly, to an ink cartridge and associated method of determining an ink volume in the ink cartridge.
2. Description of the Related Art
Over the years, a variety of ink cartridge configurations have been developed, and a number of approaches have been taken to determine the ink level in an ink cartridge prior to the depletion of the ink supply within the cartridge.
One approach is to start with a known full quantity of ink and merely count the number of ejected drops until the number of ink drops ejected corresponds to a predicted number of drops associated with an empty condition. Such an approach, however, can provide erroneous results as the quantity of ink of each drop varies due to changes in ambient temperature and pressure, as well as changes in an ink jet cartridge""s nozzle opening size, printhead temperature and internal pressure.
Another approach is to warm the print cartridge printhead and ink to a predetermined temperature. The print cartridge printhead is operated at a first firing frequency to eject a volume of ink. This operation includes heating the ink and the printhead, carrying away heat in the ejected volume of ink, and conveying a volume of cooler ink to the printhead to replace the ejected volume. A first temperature change from the predetermined temperature is monitored. The same print cartridge printhead and ink are then again warmed to a predetermined temperature. The print cartridge printhead is operated at a second firing frequency that is different than the first firing frequency to eject a volume of ink. This operation includes heating the ink and the printhead, carrying away heat in the ejected volume of ink, and conveying a volume of cooler ink to the printhead to replace the ejected volume. A second temperature change from the predetermined temperature is monitored. The first and second temperature changes are compared to indicate a low ink supply that may result in the replacement of print cartridge. Such an approach, however, is complex and is wasteful of ink.
Another approach is to provide a capacitive sensor, wherein on opposing sides of an ink cartridge, a first set of plates is positioned parallel to a second set of plates. A bag containing ink is positioned between the first and the second set of plates. An electrical source applies an alternating electric field to the first and the second set of plates. A capacitance meter measures the capacitance between the first set of plates and bag and the capacitance between the second set of plates and bag. The more ink, the closer the bag is to the plates and the higher the capacitance. Such an approach, however, is dependent upon maintaining a proper relationship between the plates as the ink is depleted.
In still another approach, ink from an ink reservoir flows to a first containment chamber, which in turn flows into a second containment chamber. As the depleting local supply of ink in first containment chamber decreases, because the second containment chamber is sealed against the ambient atmosphere, a low pressure condition occurs. As the pressure drops within the containment chambers, ambient air pressure via an ambient atmosphere vent inflates a bag member based upon the increasing pressure differential. Electrical or electromagnetic devices are used individually or in combination with a pressure regulator apparatus to sense the back pressure in the containment device after the reservoir has gone dry to trigger a signal indicating a low or out-of-ink condition. In such an approach, however, the ink level measurement point is at an empty extreme of the reservoir volume, which may not give adequate warning to the user that the cartridge must be replaced.
It is known to include a foam core in an ink container to serve as a pressure regulator. FIG. 1 shows a graph depicting the relationship between ink volume (y-axis) and ink container back pressure (x-axis) in a prior art foam ink cartridge. It should be noted from FIG. 1 that the most significant changes in back pressure occur in relation to a relatively small change in ink volume, and occur before a near full level 10 (approximately one-fourth of the ink depleted) and after a near empty level 12 (approximately one-fourth of the ink remaining), and that the major change in ink volume between the near full level 10 and the near empty level 12 results in a relatively small change in back pressure.
FIG. 2 shows a graph depicting the relationship between ink volume (y-axis) and ink container back pressure (x-axis) in a prior art ink cartridge containing a bladder as a pressure regulating device. Again, it should be noted that the most significant changes in back pressure occur in relation to a relatively small change in ink volume, and occur before a near-full level 14 (approximately one-fourth of the ink depleted) and after a near empty level 16 (approximately one-fourth of the ink remaining), and that the major change in ink volume between the near full level 14 and the near empty level 16 results in a relatively small change in back pressure.
In comparing the graph of FIG. 2 with the graph of FIG. 1, however, it is noted a higher degree of backpressure change occurs above near full level 14 of FIG. 2 than occurs above near full level 10 of FIG. 1. However, in both cases, a simple sensor would be incapable of correlating a pressure change occurring within the near full or the near empty ink levels that could be meaningfully correlated to an intermediate ink volume level.
What is needed in the art is an improved ink cartridge having a replaceable ink tank for replenishing the supply of ink contained in the ink cartridge. In addition, what is needed in the art is an ink volume sensor that identifies an intermediate ink volume level so as to permit a timely and beneficial warning to the user of a depletion of the ink below a certain ink volume level well before the empty condition is reached within the ink cartridge.
One aspect of the present invention provides an improved ink cartridge having a replaceable ink tank for replenishing the supply of ink contained in the ink cartridge. The invention comprises, in one form thereof, an ink cartridge carrying a supply of ink. The ink cartridge includes a base assembly forming an ink reservoir. A first ink tank is provided having a foam core for carrying the ink, the foam core being coupled in fluid communication with the ink reservoir. A second ink tank is provided having a bladder for carrying the ink, the bladder being coupled in fluid communication with the ink reservoir and coupled in fluid communication with the first ink tank via the ink reservoir.
Another aspect of the present invention provides an ink cartridge having an ink volume sensor that identifies an intermediate ink volume level so as to permit a timely and beneficial warning to the user of a depletion of the ink below a certain ink volume level before the empty condition is reached within the ink cartridge. Thus, another form of the invention comprises a sensor provided for detecting a pressure change in the ink reservoir corresponding to a substantial depletion of the ink contained in the first ink tank while the second ink tank retains an amount of ink above a near-full level.
An advantage of the present invention is that the first ink tank can be replaced multiple times during the life of the ink cartridge.
Another advantage is that the first tank can be replaced any time after the first tank is determined to be substantially empty but before the second ink tank is empty, thereby reducing the number of operator interactions with the ink cartridge.
Another advantage of the present invention is that an intermediate ink volume level of the ink cartridge can be identified so as to permit a timely and beneficial warning to the user of a depletion of the ink below a certain ink level well before the empty condition is reached within the ink cartridge.
Another advantage is that a simple sensor can be used in detecting the intermediate ink level associated with the ink cartridge.